HELP Please...it caught fire

[inline300]

Thanks kenny, Ill check out the link.

I was kidding about the port/polish...kinda. :biggrin:


I checked the valve movement, they seem to be seating very well. Ill double check that more closely when I install the head gasket. Good idea, thanks.

 

[inline300]

Update. Still revs way too high at all throttle positions.

This is what I know.

Carb is clean, fuel is new. float/needle/seat work as you would expect.

Intake gaskets new.

Head gasket new.

Valves were seating just fine.

Oil level is normal.


If I start the engine, and hold the throttle blade closed, the engine rpms will go low like you would expect and run at a low rpm almost die out, however, if you open the throttle just a hair bit more, the rpm of the engine climbs to an excessive level. You can have the throttle lever set on slow or fast and it makes no difference.

Im not clear what the engine governor is supposed to do, I know limit rpm, but in what way? As wide open throttle is wide open throttle, how would the governor limit rpm? I read a method to adjust the governor. I loosened the arm from the shaft, set the engine throttle to wide open but before the choke would close, took a screwdriver, turned the governor shaft clockwise, then tightened the governor arm down. This made no significant change.

Right now Im at a loss, have to do some more reading but if anyone has a suggestion, throw it my way.

Thanks

 

[KennyV]

Here is a quick link for setting the governor...
Understanding and Adjusting your Governor on a small engine
and here is a youtube video
YouTube - Briggs and Stratton Governor set up and adjustment
this is on a typical set up...

If the governor is not able to control the RPM with the linkage to the carb... I'm wondering if you have the right carb on the engine? Someone may have changed the carb &/or the linkage ??
Keep at it ... you will eventually find what is causing these problems... :smile:KennyV

 

[briggs]

this has me baffled ..I did see this on a Tecumseh engine once it turned out to be the carb it self ..The throttle shaft had enough slop in it to suck air and cause it to over rev ...I dont have my book here with me or i would go threw it and see what i could find... truly a brain teaser here

 

[inline300]

Its the oem carb, it seems to match the photos Ive found for the engine. Think I need some help double checking the linkage though.

On small 4 stroke engines, the carb throttle blade should be fully closed in the slowest position, correct?



The throttle blade should be fully open in the fastest position?

 

[briggs]

can you post a pic for me i would like to see the carb .....

 

[RobertBrown]

Ah, I still think it was good luck. This old mower cuts and looks suprisingly good, I wouldnt hesitate to just drop a new motor in it.

good thing you didn't put it in your garage before it caught fire.

 

[inline300]

Photos with captions/ questions.

All the parts are stock, including the carb, I verified it at partstree dot com

briggs&stratton 286707-0437-01

Keep in mind, the choke is missing.

on a side note, parts tree wants 35 dang dollars for a choke shaft, holy crap. I could pay a machinist to make one for less or hand craft one from a piece of stock with a file. lol

 

[briggs]

how far is this screw in it sets the position of your throttle and gov also ..if its screwed in to far it will rev high..The spring is on the linkage it looks good .I would also look at the throttle cable to make sure its set proper so it can open and close all the way ..I have the same carb on my 12hp I/C brigs ..I wont be at my shop till thur i ..If you dont have it fixed by then i will send you pics of mine and send you the info right out my shop manual

 

[inline300]

I made some progress today, kinda having what you have in mind Briggs, I starred and starred some more at the linkage and I finally realized, someone had bent the linkage stop back, not giving it full travel, so slow was more like part to mid throttle.

So the good news, the throttle linkage is squared away, and it will idle reasonably low.

The bad news, the idle is kinda higher than expected and once you crack the throttle open to a hair below part throttle, the engine wants to rev itself to death. So and fast speeds are accomplished with about 1/2" movement of the throttle lever, as opposed to the 2" potential travel of the speed lever.

Out of curiosity, I turned the airscrew all the way in while it was idling, this shoulda killed it but it kept running.

This makes me think air leak somewhere, so the best I know to do right now, is to start over, Im gonna tear the carb apart, clean, soak, blow air, perform ritual dances and give it the royal treatment and replace every thing thats not made of metal between the cylinder head and airfilter. :biggrin

Sound good?


And just so Im 100% sure, if the throttle lever is set to the fastest speed, the carb butterfly should be fully open or no? Im thinking no, as I believe the governor is meant to increase the engine speed by opening the throttle, if the engine is put under load, say cutting tall grass all of a sudden, so Im thinking if the throttle is open all the way under the fast lever setting, then the governor cant open the throttle any more? Thoughts?



Have another question, just a general mower question, the mower I have been using, has a 18 hp briggs v-twin engine, any chance the 12.5 and 18hp would use the same mounting points/drive gears? Cause I wouldnt be opposed to doing an engine swap. :biggrin: Funny thing is, the neighbor on the other side of me give that mower to me, he thought the transaxle was fried, but I replaced some belts and have been using it ever since, its an old one but it runs pretty good.